Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 201240

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
740 AM EST Tue Nov 20 2018


Light snow and snow showers follow the cold front out of SE Michigan
during early morning. High pressure building strongly into the Ohio
valley extends into Lower Michigan through early afternoon and
promotes improvement to VFR with the help of a 330 degree wind
downsloping from northern Lower Michigan. A broken VFR ceiling could
even become scattered for a few hours during late morning through
early afternoon. The wind backs toward the southwest quickly during
the late afternoon as high pressure slides eastward which allows
clouds to return during the evening. Ceiling starts out VFR and then
becomes MVFR with nocturnal influence and as Lake Michigan activates
stratocu production. The next cold front is then projected to move
into southern Lower Michigan late tonight preceded by gusty
southwest wind shifting northwest. The front appears moisture
starved with only widely scattered snow showers or flurries expected
through sunrise Wednesday.

For DTW... Light snow diminishes to snow showers and then comes to
and end with little additional accumulation during early morning.
Expect an improving cloud trend through the day with ceiling rising
into VFR while becoming broken around 4500 ft. Clouds decreasing to
scattered coverage is also possible during afternoon. This is due to
moderate northwest wind that remains below crosswind threshold but
likely requires NE traffic flow operations through mid afternoon.


* High for ceiling 5000 ft or less during the morning then moderate
  to low during afternoon and moderate again tonight.

* Low for northwest wind exceeding crosswind threshold today.


Issued at 313 AM EST Tue Nov 20 2018



As of 310 AM EST...Arctic boundary continues to push southeast
across the region early this morning, noted by a marked 850 hPa
temperature gradient of around -3C ahead of the boundary and -15C
across northern Lower. Arrival of northern stream PV energy coupled
with right entrance region dynamics of the polar jet has allowed for
a fairly decent FGEN response and flare up in coverage of light to
moderate snow across much of southeast Michigan. Surface
temperatures near freezing, however, have limited accumulation
potential especially on paved surfaces, despite large flake size
observed locally at the office thanks in part to efficient snow
microphysics. The result has been mainly wet roadways across the
region, with the exception of some slushy accumulation on less
traveled roads.

The boundary will continue to push across the region the remainder
of the overnight period, and be east of the immediate region by
sunrise. Light snow will continue through roughly 12z especially
south and east of a Sandusky/Flint/Owosso line, boosted in part by
the upper-level trough axis swinging through and allowing for some
ana-front post-frontal activity. Accumulation will be light in
nature, with most areas struggling to see an inch of total
accumulation that will mainly be on grassy surfaces. The exception
will be in the Thumb closer to the Lake Huron shoreline where post-
front northwesterly flow convergence will aid in some enhanced lake
effect activity to result in an inch or two of accumulation.

Despite post-front surface ridging today, plenty of cloud cover will
still be around in cold air advective flow as supported by upstream
observations. Model guidance appears to be bullish with potential
clearing late this morning into the afternoon, as hi-res soundings
continue to depict ample-enough boundary layer moisture trapped
within the inversion layer strengthened by increasing midlevel
subsidence. Not expecting a day full of dreary stratus, but likely
more in the way of early stratus giving way to broken stratocu for a
time this afternoon. The periodic breaks in sunshine will do little
to provide a bump in high temperatures due to the frigid
aforementioned 850 hPa temps. Thus, high temperatures will struggle
to reach the freezing mark for most areas north of the M-59
corridor. A brisk northwesterly wind will add to the chill in the
air as wind chills dip solidly into the teens.

Any breaks in sunshine quickly disappear by this evening, as mid and
high clouds quickly overspread the region from the north ahead of a
second frontal boundary that will progress across the region
tonight. This frontal boundary will be in association with a clipper-
type surface wave diving southeast across Georgian Bay into Ontario.
All indications continue to lead to a mainly dry frontal passage and
minimal, if any, accumulations accompanying widely scattered snow
showers. Low temperatures will only fall a few degrees from midday
highs due to increased cloud cover, with widespread mid/upper 20s
common. It will feel much colder than that as west/southwest winds
ramp up with the frontal passage and gusts of 20-30 mph are common.


The second front will act to further strengthen the thermal trough
in place over the region, with continued cold temperatures for the
midweek period. Some lake effect snow showers will be possible
Wednesday into Thursday for portions of the Thumb, otherwise dry
weather will prevail over the region as strong high pressure builds
over the central Great Lakes. High temperatures Wednesday will again
struggle to reach the freezing mark. As the high settles just east
of the region Wednesday night, there is the potential for a window
of enhanced scouring of clouds which would allow lows to plummet
well into the teens. Currently forecasting mid to upper teens for
lows Wednesday night, but if greater clearing does materialize,
would not be surprised to see some single digit lows in interior
portions of the Saginaw Valley.

Quiet, but cold weather is forecast for the Thanksgiving holiday,
with high temperatures struggling to make it into the upper 20s and
mid 20s for the Thumb. Low temperatures Thursday night will fall
into the low/mid 20s.

Friday will mark a transition day across much of the CONUS as strong
Pacific energy leads to a pattern shift and strong downstream flow
amplification over the eastern two-thirds of the country. Continued
dry weather will prevail with shortwave ridging passing by aloft.
Increasing low-level southwesterly flow will allow for a moderation
in temperatures as highs make a run at 40.


Long range guidance continues to indicate a very active pattern for
the long term period. The GFS and ECMWF are starting to come into
better agreement with the evolution of the Pacific energy ejecting
out of the Rockies and its interaction with an energized subtropical
jet. Confidence is beginning to increase that Saturday will be an
all-rain scenario as any phasing of the northern and southern
streams looks to be east of the immediate region allowing for more
mild air to remain in place. As this first system exits by Sunday,
only a brief reprieve looks to be in store as additional Pacific
energy ejecting out of the Rockies results in potentially deep low
pressure developing in the mid-Mississippi Valley. Still plenty of
time to watch this system unfold as it impacts the region for early
next week, with the exact synoptic evolution and track having
significant implications on ptype.


The Gale Watch is upgraded to a warning for tonight and Wednesday
across the open waters of Lake Huron. Small Craft Advisories are
extended through Wednesday night. A cold front exiting the central
Great Lakes this morning is leaving sub-gale northerly wind and high
waves ongoing across Lake Huron. This will be followed by a quick
progression of high pressure and backing of the wind to southwest
during the afternoon. Southwest wind then increases to near 30 knots
this evening as the next low pressure system reaches eastern Lake
Superior. This system sweeps a stronger cold front across the region
tonight which brings a 40 kt northwest gale to the open waters with
waves exceeding 15 feet through Wednesday morning. Marine conditions
remain unsettled Wednesday night as high pressure builds into the
central Great Lakes. The high moves quickly across Lake Huron during
Thanksgiving leaving increasing south wind to finish the week.




Lake Huron...Gale Warning from midnight tonight to 4 PM EST Wednesday for LHZ362-

     Small Craft Advisory until 4 AM EST Thursday for LHZ421-441>443.

     Gale Warning from midnight tonight to 10 AM EST Wednesday for

Lake St Clair...NONE.

Michigan waters of Lake Erie...NONE.




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